The following disclosure relates to printing systems. It finds particular application in conjunction with adjusting image quality in print or marking systems with multiple electrophotographic or xerographic print engines. However, it is to be appreciated that the presently disclosed exemplary embodiments are also amenable to other like applications.
Typically, in image rendering or printing systems, it is desirable that a rendered or printed image closely match, or have similar aspects or characteristics to a desired target or input image. However, many factors, such as temperature, humidity, ink or toner age, and/or component wear, tend to move the output of a printing system away from the ideal or target output. For example, in xerographic marking engines, system component tolerances and drifts, as well as environmental disturbances, may tend to move an engine response curve (ERC) away from an ideal, desired or target engine response and toward an engine response that yields images that are lighter or darker than desired.
For printing systems which include multiple printing engines, the importance of engine response control or stabilization is amplified. Subtle changes that may be unnoticed in the output of a single marking engine can be highlighted in the output of a multi-engine image rendering or marking system. For example, the facing pages of an opened booklet rendered or printed by a multi-engine printing system can be printed by different engines. For instance, the left-hand page in an open booklet may be printed by a first print engine while the right-hand page is printed by a second print engine. The first print engine may be printing images in a manner slightly darker than the ideal and well within a single engine tolerance; while the second print engine may be printing images in a manner slightly lighter than the ideal and also within the single engine tolerance. While a user might not ever notice the subtle variations when reviewing the output of either engine alone, when the combined output is compiled and displayed adjacently, the variation in intensity from one print engine to another may become noticeable and be perceived as an issue of quality by a user.
One approach to improve consistency among multiple engines is for a user to periodically inspect the print quality. When inconsistency becomes noticeable, the user initiates printing of test patches on multiple engines and scans the test patches. The scanner reads the test patches and adjusts the xerography of the engines to match. However, this approach requires user intervention and a scanner to scan the test patches. Another approach to improve image consistency among multiple engines is to print test patches with each engine of the multiple engine system and compare the test patches against one another. However, such an approach is complex as it involves substantial software development as well as elaborate scheduling of test patches to not interfere with the print job.
In addition to the variation of the overall engine response, as discussed above, variations in the color separations of a color printing system may contribute to hue shifts associated with a printed output. These variations may occur over time and result in a reduction in perceived color accuracy of a printed output.
This disclosure provides methods, systems and apparatus to control hue variation for multiple marking engine printing systems.